Semiconductor device and its manufacturing method

ABSTRACT

Improve the productivity and cost for the manufacturing of a semiconductor device referred to as a wafer level CSP. The manufacturing method for a semiconductor device related to this invention contains each of the processes that form a wiring ( 18 ) for the purpose of electrically connecting each electrode pad ( 10   a ) and external connecting terminals on top of a wafer ( 10 ) on which semiconductor elements are formed, connect conductive balls that are preformed by a separate process on top of this, and next, cover the above-mentioned wafer with a resin ( 32 ) such that the upper portion of the conductive supporting posts ( 30 ) are exposed. In a later process, solder balls ( 34 ) are arranged as external connecting terminals on the upper portion of the conductive supporting posts, and in the final process, semiconductor elements are formed by dicing the above-mentioned wafer along the boundary lines of the above-mentioned semiconductor elements.

This application is a divisional of application Ser. No. 09/826,269filed Apr. 04, 2001, now U.S. Pat. No. 6,525,424, which claims priorityfrom Japanese patent application serial number 2000-102429 filed Apr.04, 2000.

FIELD OF THE INVENTION

This invention relates to a semiconductor device of the so-called waferlevel CSP type and its manufacturing method in which the packaging of asemiconductor chip is realized in the wafer state.

BACKGROUND OF THE INVENTION

In the semiconductor device manufacturing industry, efforts arecontinuing for the purpose of further downsizing a single packagesemiconductor device. The initial effort for the purpose of realizingminiaturization of a semiconductor device reduced the size of thesemiconductor chip itself. By making the semiconductor chip smaller, thenumber of chips that could be obtained from one wafer was increased, andalong with bringing down manufacturing costs, since the movementdistance of electrons between each element could be made shorter, theoperating speed was increased. Due to the development of microscopicprocessing technology, decreasing the chip size for a semiconductordevice having the same functions became possible. The currentleading-edge design guideline is less than 0.18 μm, and by this means,it has become possible to place more than two million units on a singlesemiconductor chip.

In order to realize a miniaturization of the semiconductor device, thenext effort involved making the size of the package in which a chip issealed as close as possible to the size of the semiconductor chip ithouses. As one result related to this effort, a type of semiconductordevice was created called a chip size package (Chip Size Package:CSP) ora chip scale package (Chip Scale Package). The connecting terminals (forexample, solder balls, hereinafter, called external connectingterminals) for the printed circuit board on which the semiconductordevice is mounted form a two-dimensional arrangement on the face of asemiconductor chip, and was successful in bringing the size of thepackage close to the chip size. By decreasing the above-mentionedpackage size so as to approach the semiconductor chip size, along withthe mounting surface area becoming small, the wiring length thatconnected the terminals on the chip and the external connectingterminals became short, and by this means, in the same manner as whendecreasing the size of above-mentioned semiconductor chip itself, theoperating speed of the semiconductor device was increased.

However, even when the package size was decreased, the manufacturingcost could not be lowered very much. Because various processes for thepackaging were conducted for each individual semiconductor chip cut outfrom the wafer, even if the package size was decreased, because thenumber of processes was fixed, there were no changes in productivity.

With this background, technology that packages a semiconductor chip asis in the wafer state (hereinafter, called wafer level CSP) has beenproposed, and development is continuing in the direction of itsrealization by individual companies. Semiconductor manufacturingtechnology that executes packaging at a stage before individualsemiconductor chips are cut away from the wafer is referred to as waferlevel CSP. In wafer level CSP, since the packaging process can be doneas one unit with the wafer process, the packaging cost, and byextension, the manufacturing cost of the semiconductor, canadvantageously be greatly lowered. In regard to the further detailedcontent of wafer level CSP, please refer to the “Nikkei BP Companypublication, Nikkei Micro-device, 1998 August Issue, Pages 44 to 71.”

On the one hand, in a wafer level CSP, in the same manner as in aconventional CSP type semiconductor device, there are problems inmounting reliability in relation to the printed circuit board. Inthermal cycle tests of this type of semiconductor device, cracks aregenerated in the junction portion of the external connecting terminalsof the printed circuit board, and there are instances when the junctionis open and defective. The main cause is stress based on linearexpansion coefficient differences between the semiconductor chip made ofsilicon and the printed circuit board made of FR4 or the like, and ameans that relieves this must be devised in the design for a wafer levelCSP.

Thus, as a method that absorbs the linear expansion coefficientdifference between the above-mentioned semiconductor chip and theprinted circuit board, and by this means relieves the stress, aconstruction has been proposed wherein a metallic supporting post isformed on the wiring pattern of the semiconductor chip main face, and anexternal connecting terminal comprising a solder ball or the like isbonded on top of the said supporting post. In said semiconductor device,the main face of the above-mentioned semiconductor chip and thesurrounding of the supporting post are covered by resin. Due to the factthat the above-mentioned supporting post is interposed between theexternal connecting terminal that is directly bonded to the printedcircuit board and the semiconductor chip, the generation of theabove-mentioned stress can be relieved by means of deformation of saidsupporting post element.

However, a semiconductor device that is equipped with theabove-mentioned metallic supporting posts has the following types ofproblems.

(1) Time and expense are required in forming the metallic supportingposts on the main face of the semiconductor chip. In other words, theabove-mentioned metallic supporting posts are formed by means ofaccumulating a metal plating (for example, copper plating) on the wiringpattern. In order to relieve the above-mentioned stress, it is necessaryfor said supporting posts to have a height of more than 100 μm, and morethan two h are required to form these supporting posts by means of theplating method. In order to further improve the mounting reliability forthe semiconductor device, it is necessary to further heighten thesupporting posts, (for example, to more than 200 μm), and realization ofthat is extremely difficult from the aspects of time and cost.

-   -   (2) In the case of forming the metallic supporting posts by        means of a plating method, because their shape and material        cannot be freely selected, the degree of freedom for the design        of the target package is limited.

Therefore, the objective of this invention, in a semiconductor devicereferred to as a wafer level CSP, is to improve its productivity whileensuring its mounting reliability.

SUMMARY OF INVENTION

In order to achieve the above-mentioned objective, the semiconductordevice of this invention has a semiconductor chip having electrode padsthat are electrically connected to electrical circuits that are formedon the main surface of a semiconductor substrate, conductive supportingposts of nearly spherical shape that are provided on the above-mentionedsemiconductor chip and which are electrically connected to theabove-mentioned electrode pads, resin that is formed so that thesections of the above-mentioned electrode supporting posts are exposedon the above-mentioned semiconductor chip, and external connectingterminals that are provided on the tips of the above-mentionedconductive supporting posts.

In a preferred embodiment configuration, the above-mentioned electrodepads and the above-mentioned conductive supporting posts areelectrically connected by means of wiring that is formed onabove-mentioned semiconductor chip. Also, it is preferable that theabove-mentioned external connecting terminals be solder balls, and morepreferably, that the above-mentioned conductive supporting posts beconstructed by means of nearly spherical copper balls and solder thatcovers the surface of said copper balls. Furthermore, it is preferablethat the height of the above-mentioned conductive supporting posts bemore than 200 μm.

Also, the manufacturing method for a semiconductor device of thisinvention has a process that prepares a wafer on which semiconductorelements are formed having electrical circuits and electrode pads thatare electrically connected to said electrical circuits, a process thatforms wiring for the purpose of connecting external connecting terminalsand the above-mentioned electrode pads on the above-mentionedsemiconductor elements, a process that connects preformed conductivesupporting posts to prescribed positions of the above-mentioned wiring,a process that forms resin so that the tips of the above-mentionedconductive supporting posts on the above-mentioned semiconductor elementare exposed, a process that forms external connecting terminals on thetips of the above-mentioned conductive supporting posts, and a processthat produces semiconductor devices on which external connectingterminals are formed by dicing the above-mentioned wafer.

Also, it is preferable that the process that forms the above-mentionedresin contains a process that supplies a flexible resin on top of theabove-mentioned semiconductor chip and cures it, and a process thatexposes the tips of the above-mentioned conductive supporting posts bygrinding the upper section of the surface of the above-mentioned resinand the upper portion of the above-mentioned conductive supportingposts.

In this invention, since the forming of the supporting posts for thepurpose of the external connecting terminals can be done by carrying andconnecting conductive supporting posts to the desired positions of thewiring, supporting posts of the target height can be obtained in anextremely short time compared to that required for forming of supportingposts by means of the plating method used in the past. By this means, adegree of freedom in the design of the supporting posts [can beobtained], and in that way, supporting posts of sufficient dimensions,shape, and materials necessary for obtaining mounting reliability forthe package can be obtained.

Also, it is preferable that the above-mentioned conductive supportingposts be constructed by means of nearly spherical copper balls andsolder that covers the surface of said copper balls, and it ispreferable that the process that connects the above-mentioned conductivesupporting posts contain a process that carries the above-mentionedconductive supporting posts to prescribed positions on theabove-mentioned wiring, and a process that connects said conductivesupporting posts to prescribed positions of the above-mentioned wiringby melting the surface solder of the above-mentioned conductivesupporting posts. Furthermore, it is preferable that the process thatforms the above-mentioned external connecting terminals contain aprocess that carries solder balls to the tips of the above-mentionedconductive supporting posts, and a process that connects said solderballs to the above-mentioned conductive supporting posts by melting theabove-mentioned solder balls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) to 1(E) are views showing manufacturing processes for asemiconductor device related to one embodiment configuration of thisinvention.

FIGS. 2(F) to 2(J) are views showing manufacturing processes for asemiconductor device related to one embodiment configuration of thisinvention.

FIGS. 3(K) to 3(N) are views showing manufacturing processes for asemiconductor device related to one embodiment configuration of thisinvention.

FIGS. 4(O) to 4(R) are views showing manufacturing processes for asemiconductor device related to one embodiment configuration of thisinvention.

REFERENCE NUMERALS AND SYMBOLS AS SHOWN IN THE DRAWINGS

In the figures, 10 represents a wafer, 10 a represents an electrode pad,12 represents a photosensitive polyimide resin, 14 represents a barriermetal, 16 represents a resist, 18 represents wiring, 20 represents aprecious metal layer, 32 represents a resist, 24 represents a resist, 24a represents a window, 26 represents solder paste, 28 represents aconductive ball, 30 represents a conductive supporting post, 30 arepresents a solder ball connecting region, 32 represents a packageresin, 34 represents a solder ball, 36 represents a dicing saw, 38represents a semiconductor device, 70 represents a semiconductor device,and 71 represents a land.

DESCRIPTION OF EMBODIMENTS

Below, an embodiment of this invention will be explained using figures.In the manufacturing method for a semiconductor device related to thisembodiment, a package process is executed for a wafer on whichsemiconductor elements are formed, and finally, a packaged semiconductordevice is obtained when the wafer is diced. The manufacturing methodrelated to this embodiment configuration contains processes that executenecessary wiring on the surface of a wafer on which semiconductorelements are formed, connect conductive balls that are prepared by aseparate process beforehand on top of this, cover the wafer surface withresin, move solder balls that are external connecting terminals, andproduce individual packages by dicing the wafer along the boundary linesof the semiconductor elements. These specific processes are sequentiallyexplained by following FIG. 1(A) to FIG. 4(R). A person within thisindustry probably understands that these figures are shown in anexaggerated form for the purpose of explanation. Also, in the figures,only a cross-section of a portion of the wafer (corresponding to twosemiconductor devices) is shown, but by following each process shown inthe figures, the fact that the processes that are explained below areexecuted across the entire region of the wafer is probably understood.

Before each of the illustrated processes, normal wafer processes areexecuted, and semiconductor elements that are arrayed in a matrix formare formed on the surface of the silicon wafer. Here, a single circuitpattern on the wafer that is formed corresponding to a singlesemiconductor device is called a semiconductor element. A plurality ofelectrode pads that lead out from each semiconductor element are exposedon the wafer surface, and in a later process, each of the electrode padsand external connecting terminals are electrically connected.

In the initial process related to the embodiment configuration shown inFIG. 1(A), on the surface of the wafer (10) on which semiconductorelements were formed by above-mentioned wafer processes, a layer (12) ofa photosensitive polyimide resin is formed. This layer (12) temporarilycovers the electrode pads (10 a) across the entire region of the wafer(10). This layer (12) covers the surface of the comparatively brittlesilicon wafer, and softens impacts that are applied from outside thecompleted package that are propagated to the wafer surface. Next, in theprocess step shown in FIG. 1(B), using a photomask, regions along theboundary lines of the regions corresponding to the electrode pads (10 a)and the semiconductor elements are masked, and after the photosensitivepolyimide resin is exposed, the polyimide resin on the above-mentionedregions is removed by etching.

Next, in order to form metallic wiring on the wafer, process steps ofFIG. 1(C) to FIG. 2(J) are executed. First, in the process step shown inFIG. 1(C) after titanium tungsten (TiW) is deposited on the wafersurface by using an ion sputtering method, a barrier metal (14) such aschrome (Cr) or nickel (Ni) is formed on top of that. After that in theprocess step shown in FIG. 1(D), a resist (16) is formed by means ofphotolithography technology for the purpose of forming wiring, and inthe process step shown in FIG. 1(E), copper (Cu) is plated on theexposed barrier metal (14), and forms the wiring (18).

Then in the process step of FIG. 2(F), after titanium tungsten (TiW) isagain deposited on the wafer surface by means of an ion sputteringmethod, a layer (20) that oxidizes with difficulty such as gold (Au),palladium (Pd) or another precious metal is vapor deposited on theabove-mentioned wiring (18). Next, in the process step shown in FIG.2(G), the above-mentioned resist (16) is removed, and in the processstep shown in FIG. 2(H), a resist (22) is again formed by means ofphotolithography technology on top of that for the purpose of conductingmetal etching. Then, in the process step shown in FIG. 2(l) etching ofthe barrier metal (14) outside the wiring sections is conducted, and inthe process step shown in FIG. 2(J)), removal of the resist (22) isagain conducted. Through the above processes, wiring (18) is formed forthe purpose of connecting conductive supporting posts on the wafer (10)and external connecting terminals.

Next, in order to form conductive supporting posts on theabove-mentioned wiring (18), the processes shown in FIGS. 3(K) to 3(N)are executed. In the manufacturing method of this invention, in order toform the conductive supporting posts on the wiring (18), conductiveballs (28) that are prepared by a separate process are used. Theconductive balls, along with being connected to the wiring (18) and thesolder balls (34) that are the later explained external connectingterminals, function so as to relieve the stress due to linear expansioncoefficient differences between the wiring side (in other words, thesemiconductor chip) and the solder ball side (in other words, theprinted circuit board) that can be generated when the package is mountedon the printed circuit board. These conductive balls are formed by aseparate process, moved onto the wafer, and the conductive supportingposts are formed by means of connecting these to the wiring (18). In oneembodiment configuration, for the conductive balls, spherical ones canbe used in which copper is used as a core, and the surface is covered bysolder.

As will be explained later, a conductive ball with this type ofconstruction provides an excellent connection between the wiring and theexternal connecting terminal by means of the solder on the outer sideand prevents reflow destruction of the shape by means of the coppercore. Because of this latter feature, as long as the connectivity of thewiring and the external connecting terminals is maintained, it isprobably all right even if the conductive balls are formed with a highlyconductive material such as copper. In this case, the conductive ballsare connected to the wiring by using a solder paste. Also, as long as aconstant shape is maintained, in other words, as long as the shape isnot greatly damaged after mounting, it is probably all right if theentire body is formed of solder. Also, for the metal core of theconductive ball, a metal other than copper can be used as long as it isa metal with a low diffusion coefficient in relation to solder, In oneembodiment configuration, the thickness of the solder around the copperis about 20 pm.

First, in the process step shown in FIG. 3(K), before connecting saidconductive balls, windows (24 a) are formed by means of resist (24) attheir positions. In other words, resist (24) is formed so as to coverthe wiring (18) on the wafer, and only the portions for the windows (24a) are removed by means of photolithography technology. By this means,the wiring is exposed at the positions of the windows (24 a), to whichthe conductive balls are connected. Next in the process step shown inFIG. 3(L), solder paste (26) is supplied by screen printing to saidwindows (24 a). Continuing, the conductive balls (28) that have beenprepared beforehand are grasped by means of a not illustrated handle,and carried on top of the windows (24 a). Then, the solder on the ballsurface and the solder paste (26) are fused by means of an en blocreflow and connected on top of the wiring (18), and spherical conductivesupporting posts are obtained.

A specialist can probably understand that the mounting method for solderballs that are used as external connecting terminals in a BGA (ball gridarray) and similar methods can also be used here. A large number ofconductive balls (28) can be grasped at one time by means of aprescribed attachment tool, and after flux is transferred to the bottomface, the conductive balls are moved on top of the windows (24 a). Inthis condition, the wafer (10) passes through a reflow furnace, and thesolder on the surface of each conductive ball (28) and the solder paste(26) within the windows (24 a) are fused, and the conductive balls (28)can be connected on top of the wiring (18). In one embodiment, thereflow is conducted under the conditions of a temperature of 240° C.maximum, and a belt speed of 0.5 m/min. In this case, the time requiredfor executing the processes shown in FIGS. 3(L) to 3(M) was about 10min. In the next process step shown in FIG. 3(N) the resist (24) thatcovers the surface of the wafer (10) is removed, and by this means, theconductive supporting posts (30) are formed on top of the wiring.

After connecting the conductive balls (28), in process (O) of FIG. 4,package resin (32) is supplied on top of the wafer (10), and isuniformly spread on the entire surface region. The height of the packageresin (32) such as to entirely cover the conductive supporting posts(30), or as in the figure, is left in a small region in the upperportion of the conductive supporting posts (30). In order to uniformlysupply the package resin (32) on top of the wafer, a spin coatingmethod, a screen printing method, or other methods for supplying theresin can be used. Also, a liquid or gel form resin (32) can be cured bymeans of a fixed time curing. At the time of reduction to practice ofthis invention, the package resin (32), preferably, is a photosensitivepolyimide resin. Next, at process (P), the entire surface of the packageresin (32) is flattened by grinding or polishing by using a grinder orother grinding device. At this time, the upper portions of theconductive supporting posts (30) are also ground, and by this means, theconductive supporting posts (30) are exposed, and smooth circularregions (30 a) are formed here. For the conductive balls (28), in thecase of using copper as a core and covering this with solder, by meansof grinding or polishing that surface, preferably, the copper of theinner section is exposed as a portion of the region (30 a). In apreferred embodiment configuration, the diameter of the conductive balls(28) that are used is, for example, 400 μm, and after connecting theseon top of the wiring, the remaining ball height when the above-mentionedgrinding is conducted is more than 200 μm, and preferably, less than 300μm.

Next, in order to conduct the connection of the solder ball (34) used asthe external connecting terminal, the process (Q) of FIG. 4 is executed.In the same manner as in the previous processes (K) to (M), after aresist is painted on top of the surface of the above-mentioned groundwafer, it is removed on top of the smooth regions of the above-mentionedconductive supporting posts by means of etching, and here, the solderpaste is filled in by means of a screen printing method. Next, thesolder balls (34) that have been formed in a separate process are movedon top of the smooth regions (30 a), and affixed by means of an en blocreflow. The solder balls (34) are fused on top of the smooth regions (30a) by means of the reflow, and are firmly bonded through the medium ofthe broad contact area of these regions (30 a). Continuing, in process(R), the wafer (10) is diced using a dicing saw (36), and packagedsemiconductor devices (38) are obtained.

Above, embodiment configurations of this invention were explainedfollowing the figures. The application range of this invention is onlylimited by the description of the patent claims, and the fact that it isnot limited to the facts shown in the above-mentioned embodimentexamples is clear. In the above-mentioned mounting configuration, anearly spherical conductive ball was used for the purpose of forming aconductive supporting pose. As long as it follows the purpose of thisinvention, to the extent that it is manufactured by separate processes,its shape can be cylindrical, conical, square post, elliptical post, orthe like.

As in the above, according to this invention, the productivity and costsfor a semiconductor device referred to as a wafer level CSP, which are aproblem because of the plating method used in the past, can be improved,while mounting reliability is maintained.

Also, according to the manufacturing method of this invention, sinceconductive supporting posts having a height of more than 200 μm can beeasily obtained, the suppression of the generation of stress thatoriginates from the linear expansion coefficient differences betweenelements becomes simple, and the mounting reliability for this type ofsemiconductor device can be improved.

1. A manufacturing method for a semiconductor device having a processthat prepares a wafer on which semiconductor elements are formed havingelectrical circuits and electrode pads that are electrically connectedto said electrical circuits, a process that forms wiring for the purposeof connecting external connecting terminals and the above-mentionedelectrode pads on the above-mentioned semiconductor elements, a processthat connects preformed conductive supporting posts to prescribedpositions of the above-mentioned wiring, said supporting postscomprising solder, a process that forms resin so that the tips of theabove-mention conductive supporting posts on the above-mentionedsemiconductor element are exposed, a process that forms externalconnecting terminals on the tips of the above-mentioned conductivesupporting posts, and a process that produces semiconductor devices onwhich external connecting terminals are formed by dicing theabove-mentioned wafer, wherein the above-mentioned conductive supportingposts are formed by means of nearly spherical copper balls and solderthat covers the surface of said copper balls.
 2. A manufacturing methodfor a semiconductor device according to claim 1 wherein theabove-mentioned process that forms the above-mentioned resin includes aprocess that supplies a resin to the above-mentioned semiconductor chipand cures it, and a process that exposes the tip sections of theabove-mentioned conductive supporting posts by grinding the surface ofthe above-mentioned resin and the upper portion of the above-mentionedconductive supporting posts.
 3. A manufacturing method for asemiconductor device according to claim 2 wherein the above-mentionedprocess that connects the conductive supporting posts includes a processthat carries the above-mentioned conductive supporting posts toprescribed positions on the above-mentioned wiring, and a process thatconnects said conductive supporting posts to desired positions for theabove-mentioned wiring by melting the solder of the surface of theabove-mentioned conductive supporting posts.
 4. A manufacturing methodfor a semiconductor device having a process that prepares a wafer onwhich semiconductor elements are formed having electrical circuits andelectrode pads that are electrically connected to said electricalcircuits, a process that forms wiring for the purpose of connectingexternal connecting terminals and the above-mentioned electrode pads onthe above-mentioned semiconductor elements, a process that connectspreformed conductive supporting posts to prescribed positions of theabove-mentioned wiring, said supporting posts comprising solder, aprocess that forms resin so that the tips of the above-mentionedconductive supporting posts on the above-mentioned semiconductor elementare exposed, a process that forms external connecting terminals on thetips of the above-mentioned conductive supporting posts, and a processthat produces semiconductor devices on which external connectingterminals are formed by dicing the above-mentioned wafer. wherein theabove-mentioned process that forms the external connecting terminalsincludes a process that carries solder balls to the tips of theabove-mentioned conductive supporting posts, and a process that connectssaid solder balls to the above-mentioned conductive supporting posts bymelting the above-mentioned solder balls.
 5. A method for manufacturinga semiconductor device, comprising the steps of: providing asemiconductor chip having electrode pads electrically connected toelectrical circuits formed on the main surface of a semiconductorsubstrate; connecting solder supporting post to the electrode pads; andforming an insulating layer to surround the solder supporting posts suchthat a top portion of said solder supporting posts is not covered bysaid insulating layer, wherein said step of connecting solder supportingposts comprises connecting solder supporting posts having supporting anon-solder core ball.
 6. The method of claim 5, further comprising thestep of connecting said electrode pads and said solder conductivesupporting posts by wiring on the semiconductor chip.
 7. The method ofclaim 5, wherein said step of forming an insulating layer comprises thesteps of depositing said insulating layer and then planarizing thedeposited layer.
 8. The method of claim 5, wherein said solderconductive supporting posts have a height greater than 200 μm.
 9. Themethod of claim 5, further comprising the step of attaching solder ballsto said solder conductive supporting posts.